We have a backup script here, creating a full backup every month and the next 30 days it deletes the old incremental, if there is any, creates a new directory with hard links to each corresponding etc. I haven't gotten behind all this yet.

But, we definitely need to clean up as we are running out of storage space! So before I go berserk and remove files, I want to find out, which files I will really delete by removing a directory.

In other words and more general:

I have 3 directories 1 2 3

Directory 1 holds files A B C D E

Directory 2 holds hardlinks A B C E

Directory 3 holds hardlinks A C E and files F G

How could I find out, how much storage I can free by deleting directory 1?